Changes

==Limitations due to maturity differences==

==Limitations due to maturity differences==

Maturity-related differences are often observed when comparing oils with each other and with source rock extracts. High-wax oils are affected most strongly by maturity. Maturity differences involving source rocks can present particular difficulties when source rock samples are extremely immature.

[[Maturation|Maturity]]-related differences are often observed when comparing oils with each other and with [[source rock]] extracts. High-wax oils are affected most strongly by maturity. Maturity differences involving source rocks can present particular difficulties when source rock samples are extremely immature.

For these reasons, and also because of the possibility of fortuitous similarities between unrelated samples, gas chromatography seldom provides definitive positive correlations. It may, however, provide fairly definitive negative correlations. When used in conjunction with other correlation parameters, it can often be valuable for positive correlations as well, as demonstrated in the following two examples.

For these reasons, and also because of the possibility of fortuitous similarities between unrelated samples, gas chromatography seldom provides definitive positive correlations. It may, however, provide fairly definitive negative correlations. When used in conjunction with other correlation parameters, it can often be valuable for positive correlations as well, as demonstrated in the following two examples.

===Maturity difference example===

===Maturity difference example===

[[:file:oiloil-and-oilsource-rock-correlations_fig8-13.png|Figure 9]] shows gas chromatograms of two oils from Wyoming. Both were sourced from the Permian Phosphoria Formation, but are reservoired in different fields. The bimodal distribution of ''n''-alkanes in the top oil is consistent with a lower level of maturity than that of the unimodal oil at the bottom. Comparison of these oils using gas chromatography for the purpose of oil–oil correlation must be done with caution because of the maturity differences.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-13.png|Figure 9]] shows gas chromatograms of two oils from Wyoming. Both were sourced from the [[Permian]] [[Phosphoria Formation]], but are reservoired in different fields. The bimodal distribution of [[Wikipedia:Alkane#Linear_alkanes|''n''-alkanes]] in the top oil is consistent with a lower level of [[Maturation|maturity]] than that of the unimodal oil at the bottom. Comparison of these oils using gas chromatography for the purpose of oil–oil correlation must be done with caution because of the maturity differences.

===Examples of maturity differences===

===Examples of maturity differences===

[[:file:oiloil-and-oilsource-rock-correlations_fig8-14.png|Figure 10]] shows gas chromatograms of saturated hydrocarbons from an immature extract of coaly organic matter (top) and an oil with a fairly high wax content believed to have been sourced from a similar facies (bottom). Both show many of the same characteristics—high wax content, odd-carbon preference in the wax range, high pristane–phytane ratio—but maturity effects have changed many of the details.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-14.png|Figure 10]] shows gas chromatograms of saturated hydrocarbons from an immature extract of coaly organic matter (top) and an oil with a fairly high wax content believed to have been sourced from a similar facies (bottom). Both show many of the same characteristics—high wax content, odd-carbon preference in the wax range, high [[pristane–phytane ratio]]—but maturity effects have changed many of the details.

==Limitations due to evaporative loss==

==Limitations due to evaporative loss==